A portable percussion power tool such as a pneumatic jackhammer employs a linearly reciprocating piston-driven anvil which rapidly and repeatedly hammers on the end of a chisel bit and impels it into a working surface. Its effectiveness relies on the inertia of the mass of its body and gravity to bring the chisel bit back into contact with the working surface after each blow. As such, the percussion power tool tends to be very heavy, typically having a weight from about 60 to 100 pounds. During a routine operation, an operator is required to repetitively lift and reposition the heavy device for next operation. When working with a tool of such weight, the operator has to endure a great physical stress and is thus prevented from being able to operate the jackhammer for an extended period of time. Furthermore, the chisel bit is also often jammed into the material being worked and requires a great deal of effort to remove, which makes the operation even more physically demanding. As a consequence, it greatly reduces the productivity but also poses a great health-risk to its operators.
Several different types of lift assist devices have been developed to reduce these physical demands by facilitating the lifting and the extracting of the equipment. U.S. Pat. No. 2,622,562 to Longenecker discloses a detachable lift assist device for a percussion power tool, such as a pavement breaker. The lift assist device is a fluid actuated lifting jack which is controlled by a throttle valve with an operating lever adjacent to one of the hand grips of the percussion power tool. When the throttle valve is engaged, actuating media is admitted into the lifting jack and provides forces to lift the percussion power tool. When the throttle valve is disengaged, the actuating media pressure is released, but the piston of the lifting jack remains in contact with the working surface. There is no retracting mechanism provided for the piston of the lifting jack in the disclosure. However, the piston can be manually pushed back to a retracted position.
U.S. Pat. No. 2,776,653 to Eaton discloses an improvement in a pneumatic drill by attaching a pair of pneumatic lifting jacks with a substantially semicircular foot to engage with a working surface for lifting the pneumatic drill. A mechanism is also provided for retracting the lifting foot upon the return of the pneumatic drill to the working position.
U.S. Pat. No. 4,548,279 to Zaruba discloses a demolition tool with an extractor for freeing a jammed demolition tool. The extractor has a pneumatic cylinder with a lifting foot. There is no retracting mechanism provided for the piston in the disclosure. The lifting foot is constantly in contact with the working surface. A flow control valve is provided to regulate the lifting speed.
U.S. Pat. No. 4,986,370 to Johnson discloses a pneumatic lift attachment for a pneumatic jackhammer for applying an upward force to the jackhammer. The lift attachment is a cylinder with a lift foot. The body of the cylinder is enclosed within a support housing which has a lift plate with a guide hole and an adjustable chain for securing a pneumatic hammer to the lift plate. Once engaged, the lifting foot is in constant, contact with the working surface.
U.S. Pat. No. 6,050,345 to Jarvinen et al. discloses an ergonomic tool which includes a jackhammer and a lift assist mechanism. The lift assist mechanism contains a slidable frame with a lifting foot attached to the lower end and a piston attached to the upper end. The piston is directly connected to the upper body of the jackhammer and not movable. The frame which contains a rodless cylinder moves and provides a lifting force to raise the jackhammer.
More than a year ago, the present inventors disclosed a prototype of a lift assist device for a percussion power tool, such, as a pneumatic jackhammer. The lift assist device contains a double acting cylinder with a lifting foot and a commercial four-way directional control valve with five ports. The actuating cylinder and the directional control valve are from commercial sources and supplied as two separate parts. The direction control valve is mounted to the top end of the cylinder using a mounting bracket and the foot is mounted to the bottom end of the cylinder. The lift assist device is then secured to the upper body of the jackhammer using the same mounting bracket. By using a double acting cylinder, the lifting foot may be retracted by redirecting the flow of the compressed air from the upper chamber to the lower chamber to prevent damages to the lift assist device when the percussion power tool is in operation. One significant limitation of this prototype is that the lift assist device is heavy with an overall weight of over 20 pounds, which adds additional unnecessary physical burdens to the operator.
However, all these previous lift assist devices are designed as a separate unit to be attached to the body of a percussion power tool. One disadvantage of such design is that the lift assist device adds additional weight and transportation of such an assembly becomes problematic. One solution to reduce the overall weight of the assembly of the percussion power tool and the lift assist device is to integrate the lift assist device into the body of a percussion power tool. Accordingly, it is an object of the present invention to provide an integrated percussion power tool with a lift assist mechanism.